Heat-exchange pipe and producing method thereof

ABSTRACT

A heat-exchange pipe that is excellent in heat-exchange property in which a metal porous body is not easily dropped off form a metal pipe; which is provided with the metal pipe and the metal porous body made by joining a plurality of metal fibers bonded to an inner-wall surface of the metal pipe; at least some of the metal fibers in the metal porous body are partially bonded to the inner-wall surface of the metal pipe along a length direction, bended on the inner-wall surface of the metal pipe, and extend to leave from the inner-wall surface.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a heat-exchange pipe configured bybonding a porous body on an inner-wall surface of a pipe and a producingmethod thereof. Priority is claimed on Japanese Patent Application No.2020-041798, filed Mar. 11, 2020, the content of which is incorporatedherein by reference.

Background Art

As a heat-exchange pipe configured by bonding a porous body on aninner-wall surface of a pipe, for example as shown in Patent Literature1, a porous aluminum composite body in which a porous aluminum body isbonded on an inner peripheral surface of an aluminum pipe which is analuminum bulk body is disclosed. The porous aluminum body in PatentLiterature 1 is made by sintering a plurality of aluminum basesubstances to be integrated, and its porosity is set in a range of 30%or more and 90% or less.

The aluminum base substances are aluminum fibers and aluminum powder andhave a structure which are bonded to each other by columnar projectionsprotruding outward. In this case, it is described that a fiber diameterof the aluminum fibers is in a range of 20 μm or more and 1000 μm orless, and that three-dimensional and isotropic gaps are maintainedbetween the aluminum fibers.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application, FirstPublication No. 2016-006226

SUMMARY OF INVENTION Technical Problem

In the porous aluminum body described in Patent Literature, since thegaps between the aluminum fibers are isotropic and the fiber diameter ofthe aluminum fibers is small, a heat exchange with an inner-wall surfaceof the pipe (aluminum pipe) is restricted, so it is difficult toexchange the heat sufficiently between an outer surface of the pipe andthe porous aluminum body. Moreover, if the bonding between the porousaluminum body and the pipe is not sufficient, the porous aluminum bodymay drop from the pipe.

The present invention is achieved in consideration of the abovecircumstances, and has an object to provide a heat-exchange pipe havingan excellent heat-exchange property and in which a metal porous bodydoes not easily drop off from a metal pipe.

Solution to Problem

A heat-exchange pipe of the present invention is provided with a metalpipe and a metal porous body which is configured by joining a pluralityof metal fibers and bonded to an inner-wall surface of the metal pipe.At least some of the metal fibers are partially bonded to the inner-wallsurface of the metal pipe for a length direction. The metal fibers whichare bonded to the inner-wall surface bend on the inner-wall surface ofthe metal pipe and extend from the inner-wall surface to leave.

Since some of the metal fibers which are in contact with the inner-wallsurface of the metal pipe are bonded, the heat is exchanged between themetal pipe and the metal porous body in a whole of the bonded parts.Moreover, since the metal fibers extend from the inner-wall surface toleave from the bonded parts between the metal pipe and the metal porousbody, the metal fibers can be arranged effectively in a center part of across-sectional surface of the metal pipe, so that the heat exchangewith a fluid flowing in the metal pipe is favorably performed.Accordingly, this heat-exchange pipe is excellent in the heat-exchangeproperty between the exterior and the interior of the pipe.

Furthermore, since the metal fibers are bonded to the inner-wall surfaceat a part of the length direction not at an end part, there is no fearof dropping off from the metal pipe and it is possible to maintain theheat-exchange performance stably for a long time.

As one aspect of the heat-exchange pipe, it is preferable that a bondingarea ratio of the metal fibers to the inner-wall surface of the metalpipe be 5% or more.

If the bonding area ratio is 5% or more, the metal fibers aresufficiently bonded to the inner-wall surface of the metal pipe, they donot drop off. If it is less than 5%, since the contact of the metalfibers to the inner-wall surface of the metal pipe is small, there is arisk that the heat exchange between the metal pipe and the metal fibersmay be small.

As another aspect of the heat-exchange pipe, a difference between anaverage area ratio of the metal fibers in a center part corresponding ahalf of an area of a transverse cross section of the metal pipe and anaverage area ratio of the metal fibers in a whole of the transversecross section is preferably in 5% or less.

In the metal porous body, the metal fibers are preferably arrangedevenly in the cross section of the metal pipe. If the metal fibers arebiased to be arranged to either of the center part or an innerperipheral wall part, a fluid is concentrated and flows in a part wherethe area ratio of the metal fibers is small in the cross section, andthe heat-exchange performance may be deteriorated. If the differencebetween the average area ratio in the center part of the cross sectionand the average area ratio in the whole cross section of the metal pipeis 5% or less, the fluid flows in the whole cross section of the metalpipe, and the heat is exchanged effectively with the metal fibers.

A producing method of a heat-exchange pipe of the present invention hasa precursor formation step of stacking a plurality of metal fibers toform a precursor, an in-pipe charging step of pushing the precursor fromone end of the metal pipe to charge into the metal pipe, and a sinteringstep of sintering the metal pipe in a state of charging the precursor;the precursor before the in-pipe charging step is formed such that anouter diameter in a state where the metal fibers are stacked is largerthan an inner diameter of the metal pipe.

By forming the outer diameter of the precursor larger than the innerdiameter of the metal pipe, when the precursor is pushed into the metalpipe, the metal fibers disposed on the outer peripheral part of theprecursor is bent, and is in contact with the inner-wall surface of themetal pipe along the length direction. In the outer peripheral part ofthe precursor, the metal fibers are provided in a state of being bent atthe inner-wall surface of the metal pipe and then extending to leavefrom the inner-wall surface. Accordingly, since the metal fibers arepartially bonded to the inner-wall surface of the metal pipe andarranged to extend in a cross-sectional direction, it is possible toproduce the heat-exchange pipe having an excellent heat-exchangeproperty.

Advantageous Effects of Invention

According to the present invention, it is possible to provide aheat-exchange pipe zo with an excellent heat-exchange property and inwhich the metal porous body is not easily dropped off from the metalpipe.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 It is a longitudinal cross-sectional view of a heat-exchange pipeof an embodiment according to the present invention.

FIG. 2 It is a transverse cross-sectional view taken along the line A-Ain FIG. 1 .

FIG. 3 It is a flowchart showing an embodiment of a producing method ofthe present invention.

FIG. 4 It is a schematic view of a metal porous body (porous aluminumsintered body).

FIG. 5 It is a schematic view of an aluminum material for sintering.

FIG. 6 It is a schematic view showing a state in which columnarprojections are made in the aluminum material for sintering.

FIG. 7 It is a schematic view showing a state of the columnarprojections.

FIG. 8 It is a schematic view showing a step of forming a precursor.

FIG. 9 It is a schematic view showing a state in which the precursor ispushed into an aluminum pipe. The left part surrounded by a circle is anenlarged view of a principal part.

FIG. 10 It is a CT image of a transverse section of the heat-exchangepipe.

FIG. 11 It is a CT image of a longitudinal section of the heat-exchangepipe.

FIG. 12 It is a CT image showing a bonded part of a porous aluminumsintered body on an inner-wall surface of the aluminum pipe.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be explained below. Aheat-exchange pipe 10 of this embodiment is, as shown in FIG. 1 and FIG.2 , configured from an aluminum pipe (corresponding to a metal pipe ofthe present invention) 20 made of aluminum or aluminum alloy and aporous aluminum sintered body (corresponding to a metal porous body ofthe present invention: herein after “a porous body”) 30 made of aluminumor aluminum alloy, charged in the aluminum pipe 20.

In the heat-exchange pipe 10, a heat source (not illustrated) which ishigh temperature or low temperature is provided outside a portion wherethe porous body 30 is charged; a gas or liquid fluid as a heat-transfermedium is flowed inside the aluminum pipe 20, and the fluid changes heatwith the heat source when passing in the porous body 30.

The aluminum pipe 20 is an ordinary pipe having a circular cross sectionformed by extrusion molding or the like of Al—Mn type alloy or the likesuch as A3003. The aluminum pipe 20 has, for example, 5 mm to 150 mm ofan outer diameter and 0.8 mm to 10 mm of a wall thickness.

The porous body 30 is, as shown in FIG. 4 , integrated by sintering aplurality of aluminum base substances (metal substances) 31; a porosityis set in a range of 30% or more and 90% or less. As the aluminum basesubstances 31, a mixture of aluminum fibers 31 a (metal fibers) andaluminum powder particles 31 b is used.

On outer surfaces of the aluminum base substances 31, a plurality ofcolumnar projections 32 protruding outward are formed; the plurality ofthe aluminum base substances 31 are joined by base substance joint parts35. The base substance joint parts 35 are parts where the columnarprojections 32 are joined to each other, parts where the columnarprojections 32 and surfaces of the aluminum base substances 31 arejoined, and parts where the surfaces of the aluminum base substances 31are joined to each other.

In the base substance joint parts 35, eutectic element compounds 17containing Ti—Al type compounds 16 and eutectic elements thateutectic-reactions with Al exist. In this embodiment, the Ti—Al typecompounds 16 are compounds of Ti and Al: more specifically, they areAl₃Ti intermetallic compounds.

As the eutectic elements that eutectic-react with Al, for example, Ag,Au, Ba, Be, Bi, Ca, Cd, Ce, Co, Cu, Fe, Ga, Gd, Ge, In, La, Li, Mg, Mn,Nd, Ni, Pd, Pt, Ru, Sb, Si, Sm, Sn, Sr, Te, Y, Zn, and the like, areexemplified. Among them, Ni, Mg, Cu, and Si are preferable.

In this porous body 30, the aluminum base substances 31 are bonded toeither or both the other aluminum base substances 31 or the inner-wallsurface of the aluminum pipe 20.

The aluminum fibers 31 a joined to the inner-wall surface of thealuminum pipe 20 are joined in a state of being in contact along thelength direction for a range of a prescribed length (in other words, thealuminum fibers 31 a are joined at a part in the length direction to theinner-wall surface); the middle of the aluminum fibers 31 a are bendedon the inner-wall surface of the aluminum pipe 20, and the rest which isnot in contact with the inner-wall surface extends and leaves from theinner-wall surface.

It is preferable that the aluminum fibers 31 a be bended at right angleto the joined part to the inner-wall surface of the aluminum pipe 20 andextend perpendicular from the inner-wall surface of the aluminum pipe20. However, if they are separated from the inner-wall surface of thealuminum pipe 20, it is not necessary to be perpendicular to theinner-wall surface. Moreover, it is applicable that one aluminum fiber31 a that is joined in a state of being in contact at two or moreportions to the inner-wall surface of the aluminum pipe 20 exists.

Since the aluminum fibers 31 a are joined to the inner-wall surface ofthe aluminum pipe 20 in a state of being in contact in the range of theprescribed length, a joined area (total area) of the aluminum fibers 31a to the aluminum pipe 20 is preferably 5% or more to an area of theinner-wall surface of the aluminum pipe 20 in a region E where theporous body 30 is provided.

That is, in the region E where the porous body 30 is provided, where abonding area ratio to the wall surface is a percentage of (the joinedarea of the aluminum fibers 31 a)/(the area of the inner-wall surface ofthe aluminum pipe 20), it is preferable that the bonding area ratio ≥5%.If the bonding area ratio is less than 5%, the aluminum fibers 31 a areweakly joined to the aluminum pipe 20 and dropped off from the joinedpart, so that the heat transference is deteriorated and there is a riskthat the porous body 30 is dropped off from the inner-wall surface ofthe aluminum pipe 20.

Since the porous body 30 does not perform effective heat transfer if thealuminum base substances 31 are unevenly distributed near the inner-wallsurface of the aluminum pipe 20, it is preferable that the aluminum basesubstances 31 are arranged to be dispersed throughout thecross-sectional area of the aluminum pipe 20.

Specifically, as shown in FIG. 2 , a difference between an average arearatio of the aluminum fibers 31 a in a region F of a center partcorresponding a half of an area of the cross section of the aluminumpipe 20 and an average area ratio of the aluminum fibers 31 a in aregion G of the entire cross section is 5% or less. If the difference ofthe average area ratios exceeds 5%, in the porous body 30, the aluminumbase substances 31 may be unevenly distributed on the inner-wall surfaceof the aluminum pipe 20.

There are portions where the aluminum base substances 31 and theinner-wall surface of the aluminum pipe 20 are joined via the columnarprojections 32. In the joined portions, the above-described eutecticelement compounds 17 are present, containing Ti—Al type compounds 16 andeutectic elements that eutectic-react with Al.

Next, a producing method of the heat-exchange pipe 10 of the presentembodiment will be explained. FIG. 3 shows the flowchart.

As the aluminum base substances 31, as described above, the aluminumfibers 31 a and the aluminum powder particles 31 b are used.

Here, the aluminum fibers 31 a of the aluminum base substances 31 aremade by a melt-spinning method. That is, a material made of aluminum oraluminum alloy is heated and melted, and extruded from a nozzle into theair or water at a constant rate to cool and solidify it; and it is cutat a prescribed length.

A fiber diameter R of the aluminum fibers 31 a is in a range of 20 μm ormore and 1000 μm or less; preferably, in a range of 50 μm or more and500 μm or less. A fiber length L of the aluminum fibers 31 a is in arange of 0.2 mm or more and 100 mm or less; preferably, in a range of 1mm or more and 50 mm or less.

The aluminum fibers 31 a can be in a range of 4 or more and 2500 or lessof a rate L/R between the length L and the fiber diameter R, forexample.

If the fiber diameter R of the aluminum fibers 31 a is less than 20 μm,the joined area between the aluminum fibers to each other is small, anda sintering strength may be insufficient. On the other, if the fiberdiameter R of the aluminum fibers 31 a exceeds 1000 μm, the number ofcontact points where the aluminum fibers are in contact with each otherlacks and the sintering strength may also lack.

If the ratio L/R between the length L and the fiber diameter R of thealuminum fibers 31 a is less than four, when the aluminum fibers 31 aare piled and arranged in the producing method of the porous aluminumsintered body, it is difficult to make a bulk density DP of the porousbody 30 to be 50% or less of a true density DT of the aluminum fibers,and it may be difficult to obtain the porous body 30 having the highporosity. On the other, if the ratio L/R between the length L and thediameter R of the aluminum fibers 31 a exceeds 2500, the aluminum fiberscannot be dispersed evenly, and there may be a risk that the porous body30 having the even porosity is not easily obtained.

In order to further increase the porosity, the ratio L/R between thelength L and the fiber diameter R of the aluminum fibers 31 a ispreferably 10 or more. In order to obtain the porous body 30 having amore uniform porosity, the ratio L/R between the length L and thediameter R of the aluminum fibers 31 a is preferably 500 or less.

Atomized powder can be used as the aluminum powder particles 31 b. Aparticle diameter of the aluminum powder particles 31 b is in a range of5 μm or more and 500 μm or less, preferably in a range of 20 μm or moreand 200 μm or less.

By adjusting a mixing ratio of the aluminum fibers 31 a and the aluminumpowder particles 31 b, the porosity can be adjusted. That is, byincreasing the ratio of the ratio of the aluminum fibers 31 a, theporosity of the porous body 30 can be increased. For example, it ispreferable that the ratio of the aluminum powder particles 31 b be 15%by mass or less and the ratio of the aluminum fibers 31 a be 85% by massor more in the aluminum base substances 31.

As the aluminum fibers 31 a and the aluminum powder particles 31 b,other than pure aluminum, aluminum alloy may be used. For example,aluminum base substances made of A3003 alloy (Al-0.6% by mass of Si-0.7%by mass of Fe-0.1% by mass of Cu-1.5% by mass of Mn-0.1% by mass of Znalloy), A5052 alloy (Al-0.25% by mass of Si-0.40% by mass of Fe-0.10% bymass of Cu- 0.10% by mass of Mn-2.5% by mass of Mg alloy-0.2% by massCr-0.1% by mass of Zn alloy) that are regulated by JIS or the like canbe suitably used.

It is not necessary that the aluminum fibers 31 a and the aluminumpowder particles 31 b have the same composition. For example, thealuminum fibers 31 a made of pure aluminum and the aluminum powderparticles 31 b made of JIS A3003 alloy can be appropriately adjusted inaccordance with the purpose.

Titanium powder particles 42 and eutectic element powder particles 43are fixed to the aluminum base substances 31 composed of the aluminumfibers 31 a and the aluminum powder particles 31 b configured asdescribed above to make an aluminum material 40 for sintering.

The aluminum material 40 for sintering includes, as shown in FIG. 5 ,the aluminum base substances 31 (in FIG. 5 FIG. 6 , the aluminum fiber31 a is shown in the left and the aluminum powder particle 31 b is shownin the right) and the plurality of titanium powder particles 42 and theeutectic-element powder particles (nickel powder particles, magnesiumpowder particles, copper powder particles, and silicon powder particles)43 fixed on the outer surface of the aluminum base substances 31.

As the titanium powder particles 42, either one of or bothmetal-titanium powder particles and titanium hydride powder particlescan be used. As the eutectic-element powder particles 43, metal-nickelpowder particles, metal-magnesium powder particles, metal-copper powderparticles, metal-silicon powder particles, and alloy powder of these areused.

In the aluminum material 40 for sintering, a content of the titaniumpowder particles 42 is in a range of 0.01% by mass or more and 20% bymass or less.

A particle diameter of the titanium powder particles 42 is in a range of1 μm or more and 50 μm or less, preferably in a range of 5 μm or moreand 30 μm or less. Since the particle diameter of the titanium hydridepowder particles can be made smaller than the metal titanium powderparticles, it is preferable to use the titanium hydride powder particlesin a case of making the particle diameter of the titanium powderparticles 42 fixed on the outer surface of the aluminum base substrates31 minute.

Gaps between the titanium powder particles 42 and 42 fixed on the outersurface of the aluminum base substances 31 are preferably in a range of5 μm or more and 100 μm or less.

Contents of components of the eutectic-element powder particles 43 inthe aluminum material 40 for sintering are as followings: the nickelpowder particles are in a range of 0.01% by mass or more and 5.0% bymass or less, the magnesium powder particles are in a range of 0.01% bymass or more and 5.0% by mass or less, the copper powder particles arein a range of 0.01% by mass or more and 5.0% or less, and the siliconpowder particles are in a range of 0.01% by mass or more and 15.0% bymass or less.

The nickel powder particles are in a range of 1 μm or more and 20 μm orless, preferably in a range of 2 μm or more and 10 μm or less. Themagnesium powder particles are in a range of 20 μm or more and 500 μm orless, preferably in a range of 20 μm or more and 100 μm or less. Thecopper powder particles are in a range of 5 μm or more and 500 μm orless, preferably in a range of 20 μm or more and 100 μm or less. Thesilicon powder particles are in a range of 5 μm or more and 200 μm orless, preferably in a range of 10 μm or more and 100 μm or less.

As shown in FIG. 3 , steps are carried out in order. First, in thenormal temperature, the aluminum base substances 31 composed of thealuminum fibers 31 a and the aluminum powder particles 31 b, thetitanium powder particles 42, and the eutectic-element powder particles(e.g., the nickel powder particles, the magnesium powder particles, thecopper powder particles, and the silicon powder particles) 43 are mixed(a mixing step).

At this time, a binder solution is sprayed. As a binder, it ispreferable to be burned and resolved when it is heated to 500° C. in theair: in particular, it is preferable to use an acrylic resin and acellulose polymer. As a solvent of the binder, various solvents such asan aqueous solvent, an alcohols solvent, or an organic solvent can beused.

In this mixing step, for example, using various blenders such as anautomatic mortar, a pan-type oscillating granulator, a shaker mixer, apot mill, a high-speed mixer, a V-type mixer or the like, the aluminumbase substances 31, the titanium powder particles 42, and theeutectic-element powder particles 43 are mixed while fluidizing.

Next, a mixture which is obtained in the mixing step is dried (a dryingstep). By the mixing step and the drying step, on the aluminum basesubstances 31 shown in the upper part of FIG. 5 that is composed of thealuminum fibers 31 a and the aluminum powder particles 31 b, thetitanium powder particles 42 and the eutectic-element powder particles43 are dispersed and fixed as shown in the lower part, to produce thealuminum material 40 for sintering which is the present embodiment.

Next, the aluminum material 40 for sintering is sprayed into acylindrical carbon container 50 shown in FIG. 8 and filled withoutadding pressure (a material-spraying step). The carbon container 50includes, for example, a cylindrical body 51 and a bottom lid 52 thatcan open and close a bottom part of the cylindrical body 51. Thecylindrical body 51 is formed to have an inner diameter larger than aninner diameter of the aluminum pipe 20.

By spraying the aluminum material 40 for sintering on the bottom lid 52,the aluminum fibers 30 a of the aluminum base substances 31 are arrangedso that most of the aluminum fibers 30 a lie on the bottom lid 52, inother words, substantially in parallel with a surface of the bottom lid52, and is sequentially piled from below.

In a state in which the aluminum material 40 for sintering is filled upto a predetermined height in the carbon container 50, they are chargedinto a degreasing furnace and heated in the atmosphere to remove thebinder (a binder removal step).

The process from the mixing step to the binder removal step explainedabove is a precursor formation step.

Then, the aluminum material 40 for sintering is taken out from thecarbon container 50 and filled in the aluminum pipe 20 (an in-pipecharging step). The aluminum material 40 for sintering becomes a stateof mutually fixed in the carbon container 50 in the binder removal step;by being taken out from the carbon container 50, it becomes a precursor41 having a disc shape or a columnar shape in accordance with the filledheight. The precursor 41 has an outer diameter larger than the innerdiameter of the aluminum pipe 20. The outer diameter is preferablylarger than the inner diameter of the aluminum pipe 20 at 1 mm or moreand 10 mm or less, for example.

Since the precursor 41 has the larger outer diameter than the innerdiameter of the aluminum pipe 20, as shown in FIG. 9 , using a push-inrod 53, when the precursor 41 is loaded into the aluminum pipe 20 so asto pushing the precursor 41 from one end of the aluminum pipe 20, asshown in a double-dotted chain lines in FIG. 9 , an outer peripheralpart of the precursor 41 is bended at substantially orthogonal on theinner-wall surface of the aluminum pipe 20, and the outer peripheralpart that is bended is in close contact with the inner-wall surface ofthe aluminum pipe 20.

On the contact portions to the inner-wall surface of the aluminum pipe20, the aluminum fibers 31 a of the precursor 41 is in contactsubstantially along an axial direction of the aluminum pipe 20. Insidethe aluminum pipe 20, the aluminum fibers 31 a leave from the inner-wallsurface of the aluminum pipe 20 and extend along substantially a crosssectional direction of the aluminum pipe 20.

Although a thickness of the precursor 41 may be a lump of a sizecorresponding to a loading region E of the porous body 30 provided inthe aluminum pipe 20 in the heat-exchange pipe 10 as a product, aplurality of precursors 41 having a thickness smaller than a thicknessof a final product may be prepared for one product, or a plurality ofthe precursors 41 may be pushed into the aluminum pipe 20 one by one, ora plurality of the precursors 41 may be pushed into the aluminum pipe 20to be loaded.

Thereafter, the aluminum pipe 20 loaded with the precursor 41 is chargedin a sintering furnace in at an inert gas atmosphere, and held in atemperature range of 575 to 665° C. for 0.5 to 60 minutes in accordancewith the kind and addition amount of the added eutectic-element powderparticles 43 (sintering step). The retention time is preferably 1 to 20minutes.

In the sintering step, although the aluminum base substances 31 in thealuminum material 40 for sintering formed into the precursor 41 ismelted, since oxide films are formed on the surface of the aluminum basesubstances, the melted aluminum is held by the oxide films and the shapeof the aluminum base substances 31 is maintained.

In portions of the outer surface of the aluminum base substances 31where the titanium powder particles 42 are fixed, the oxide films arebroken by the reaction with titanium, and the melted aluminum inside isejected outward. The ejected melted aluminum generates a compound havinga high melting point and is solidified by the reaction with titanium.

As a result, as shown in the lower stage of FIG. 6 , a plurality ofcolumnar projections 32 are formed on the outer surface of the aluminumbase substances 31. In the columnar projection 32, a Ti—Al type compound16 is present; and growth of the columnar projections 32 more thannecessary is suppressed by the Ti—Al type compound 16.

In a case of using titanium hydride as the titanium powder particles 42,the titanium hydride is decomposed at about 300 to 400° C., and thegenerated titanium reacts with the oxide film on the surface of thealuminum base substances 31.

In the present embodiment, by the eutectic-element powder particles 43fixed on the outer surface of the aluminum base substances 31, portionswhere the melting point falls down are locally formed on the aluminumbase substances 31. Accordingly, in accordance with the types and theaddition amount of the added eutectic-element powder particles 43, evenunder a condition of comparative low temperature such as 575 to 655° C.,the columnar projections 32 are reliably formed.

The adjacent aluminum base substances 31 and 31 are joined via thecolumnar projections 32 of each other by integrated in a melted state orsolid-phase sintered, and the porous body 30 in which the plurality ofthe aluminum base substances 31 and 31 are joined via the columnarprojections 32 is produced as shown in FIG. 4 .

In the base substance joint parts 35 where the aluminum base substances31 and 31 are joined via the columnar projections 32, as shown in FIG. 7, the Ti—Al type compound (Al₃Ti intermetallic compound) 16 and theeutectic-element compound 17 exist.

On the inner-wall surface of the aluminum pipe 20, the precursor 41 isbended and in contact at the outer peripheral part, some of the aluminumfibers 31 a of the aluminum base substances 31 are in contact along thelength direction, and the aluminum fibers 31 a and the aluminum pipe 20are joined by sintering in this state. Accordingly, the aluminum fibers31 a are joined in a state of being in linearly contact.

Some of the columnar projections 32 of the aluminum base substances 31are also joined to the aluminum pipe 20. In a case in which the titaniumpowder particles 42 and the eutectic-element powder particles 43 are incontact with the surface of the aluminum pipe 20, the columnarprojections 32 are formed also from the surface of the aluminum pipe 20,and the aluminum pipe 20 and the porous body 30 are joined.

In the heat-exchange pipe 10 having above-described structure, since thealuminum fibers 31 a of the porous body 30 are bended on the inner-wallsurface of the aluminum pipe 20 and some of them are joined to theinner-wall surface of the aluminum pipe 20 in a state of being inlinearly contact, the heat exchange is rapidly carried out between theporous body 30 and the inner-wall surface.

In the inside of the aluminum pipe 20, since the aluminum fibers 31 aextend toward a direction leaving from the inner-wall surface of thealuminum pipe 20, e.g., along the radial direction, the heat-exchangeperformance with the heat-transfer medium is also excellent.

Moreover, since the aluminum fibers 31 a are joined on the inner-wallsurface of the aluminum pipe 20 in the state of being in contact alongthe length direction, it is not easily peeled off from the aluminum pipe20, and it is possible to maintain the heat-exchange performance stablyfor a long time.

Since the Ti—Al type compound 16 exists in the portion which is joinedby the columnar projections 32, the oxide films on the surface of thealuminum pipe 20 and the porous body 30 are removed by this Ti—Al typecompound 16, so that the joining strength between the aluminum pipe 20or the porous bodies 30 themselves is improved.

Furthermore, since growth of the columnar projections 32 is restrainedby the Ti—Al type compound 16, it can be restrained that the meltedaluminum from ejecting to the porous body 30 to maintain the porosity ofthe porous body 30.

Particularly, in the present embodiment, since Al₃Ti exists as the Ti—Altype compound 16, the oxide film formed on the surface of the aluminumpipe 20 and the porous body 30 is reliably removed, and it is possibleto drastically improve the joining strength between the aluminum pipe 20and the porous body 30.

In the present embodiment, since the eutectic-element compound 17 existsin the columnar projections 32, the melting point of the aluminum basesubstances 31 is partially reduced so that the columnar projections 32tend to be formed thick; as a result, the joining strength between thealuminum pipe 20 and the porous body 30 can be further improved.

In the present embodiment, since the content of the titanium powderparticles 42 is 0.01% by mass or more and 20% by mass or less in thealuminum material 40 for sintering, the columnar projections 32 can beformed with appropriate intervals on the outer surface of the aluminumbase substances 31, so it is possible to reliably join the aluminum pipe20 and the porous body 30.

In the present embodiment, since the interval between the plurality oftitanium powder particles 42 and 42 fixed on the outer surface of thealuminum base substances 31 is in a range of 5 μm or more and 100 μm,the interval between the columnar projections 32 is appropriate, and itis possible to obtain the porous body 30 having sufficient strength andhigh porosity.

In the present embodiment, since the content of the eutectic-elementpowder particles 43 are in a range of 0.01% by mass or more and 5.0% bymass or less, the magnesium powder particle are in a range of 0.01% bymass or more and 5.0% by mass or less, the copper powder particles arein a range of 0.01% by mass or more and 5.0% by mass or less, and thesilicon powder particles are in a range of 0.01% by mass or more and15.0% by mass or less in the aluminum material 40 for sintering;accordingly, the portions where the melting point is partially reducedin the aluminum base substances 31 can be formed with the appropriateintervals and the unnecessary melted aluminum can be restrained fromflowing out, so it is possible to obtain the porous body 30 having thesufficient strength and the high porosity.

In accordance with the kinds and the addition amount of the addedeutectic-element powder particles, the columnar projections 32 isreliably formed even in the comparatively low temperature condition suchas 575 to 665° C., so that the temperature condition for the sinteringstep can be set low.

In the present embodiment, since the aluminum fibers 31 a and thealuminum powder particles 31 b are used as the aluminum base substances31, by adjusting the mixture ratio of them, the porosity of the porousbody 30 can be controlled.

The porous body 30 of the present embodiment has the porosity in a rangeof 30% or more and 90% or less, so that a surface area of a porousaluminum composite body 10 used as a heat-transfer member can bemaintained, and the heat-transfer efficiency can be drasticallyimproved.

The present invention is not limited to the above-described embodimentsand various modifications may be made without departing from the scopeof the present invention.

For example, in the above embodiment, the pipe is made of aluminum andloaded with the porous aluminum sintered body having the aluminum fibersand aluminum powder; however, it is not limited to aluminum and variousmetals which can be sintered can be used. In the present invention, ametal porous body in which a plurality of metal fibers are joined isbonded to the metal pipe.

Although the metal porous body is configured from a mixed body of themetal fibers and the metal powder in the above-described embodiment, themetal porous body may be formed from only the metal fibers. In thatcase, the metal fibers are mutually joined by sintering and themetal-wire fibers and the inner-wall surface of the metal pipe arebonded.

The metal pipe is not limited to have the circular cross section, butthe cross section may be polygon or the like.

EXAMPLES

An aluminum pipe that is made of JIS A3003 aluminum alloy; aluminumfibers and aluminum powder as aluminum base substances; titanium powder;and Mg powder as eutectic-element powder were prepared. An innerdiameter of the aluminum pipe was 18 mm.

Many kinds of the aluminum fibers were manufactured in a range of 300 μmof a diameter and 10 mm to 25 mm of a length.

Aluminum material for sintering was produced by mixing the aluminum basesubstances, the titanium powder and the eutectic-element powder, and aprecursor of disk shape with a diameter 22 mm was produced. Theprecursor was pushed into the aluminum pipe, and then they were sinteredat 600° C. for 30 minutes, to produce a heat-exchange pipe in which theporous aluminum sintered body was joined on the aluminum pipe in a rangeof a predetermined length was produced.

An X-ray CT (computed tomography) image of the cross section of theobtained heat-exchange pipe was analyzed using an image processingsoftware (ExFact VR 2.1 made by Nihon Visual Science, Inc.) as follows.

An average area ratio occupied by the porous aluminum sintered body inthe whole cross section and an average area ratio occupied by the porousbody in the center part region of the cross section were measured.Regarding the cross section, using an orthogonal cross-sectionalfunction of the software, an average value of results of extracting 36images at about 0.7 mm intervals and analyzing them was shown.

For a bonding area ratio of the porous aluminum sintered body on theinner-wall surface of the aluminum pipe, using a cylindrical panoramicfunction of the software, cylindrical panoramic images of portions wherethe porous aluminum sintered body and the aluminum pipe are joined wereextracted, and a ratio of an area occupied by the portions where theporous aluminum sintered body was joined for the whole area wasmeasured.

Furthermore, a columnar rod having an outer diameter 14 mm was insertedinto the aluminum pipe, it was observed whether the porous aluminumsintered body was peeled from the aluminum pipe and dropped off byadding 10 N of force.

These results are shown in Table 1.

TABLE 1 CROSS SECTION WALL AVERAGE AREA SURFACE RATIO (%) BONDING CENTERAREA PEEL OFF No. WHOLE PART RATIO (%) OBSERVATION 1 20.0 23.6 19.0 NO 220.2 15.4 12.4 NO 3 19.1 16.6 6.4 NO 4 20.5 25.4 2.0 SLIGHTLY PEELED 510.3 11.2 9.3 NO 6 9.8 13.5 6.1 NO 7 8.9 13.2 1.2 SLIGHTLY PEELED 8 27.622.9 32.1 NO 9 29.7 28.5 24.5 NO 10 28.5 29.9 11.1 NO 11 27.9 29.7 4.5SLIGHTLY PEELED

Although there were some slight peelings in the drop-off test of theporous aluminum body, this is a severe test which is impossible in anormal flowing of a fluid, and it is considered not to be a practicalproblem. Moreover, if it is firmly bonded on the aluminum pipe likethis, the heat-exchange property is also considered to be excellent.

CT images of No. 1 show a transverse cross-sectional view in FIG. 10 , avertical cross-sectional view in FIG. 11 , and the inner-wall surface ofthe aluminum pipe in FIG. 12 . In these drawings, the porous aluminumsintered body is white portions excepting an outermost peripheralportion in FIG. 10 and upper and lower thick linear portions in FIG. 11. In FIG. 10 , more portions in which the porous aluminum sintered bodyis long (the aluminum fibers) exist than in FIG. 11 . In FIG. 11 , a lotof spots of the transvers cross section of the aluminum fibers appearsin spots. Moreover, as seen from FIG. 12 , also on the inner-wallsurface of the aluminum pipe, the long portions of the porous aluminumbody (the aluminum fibers) are bonded.

INDUSTRIAL APPLICABILITY

A heat-exchange pipe in which the heat-exchange property is excellentand a metal porous body is not easily dropped off from the metal pipecan be provided.

REFERENCE SIGNS LIST

10 Heat-exchange pipe

20 Aluminum pipe (Metal pipe)

30 Porous aluminum sintered body (Metal porous body)

31 Aluminum base substance

31 a Aluminum fiber

31 b Aluminum powder

40 Aluminum material for sintering

41 Precursor

50 Carbon container

53 Push-in rod

1. A heat-exchange pipe comprising a metal pipe having a circular crosssection and a metal porous body which is configured by joining aplurality of metal fibers and bonded to an inner-wall surface of themetal pipe, wherein at least some of the metal fibers are partiallybonded to the inner-wall surface of the metal pipe for a lengthdirection, and the metal fibers which are bonded to the inner-wallsurface bend on the inner-wall surface of the metal pipe and extend fromthe inner-wall surface to leave.
 2. The heat-exchange pipe according toclaim 1, wherein a bonding area ratio of the metal fibers to theinner-wall surface of the metal pipe is 5% or more.
 3. The heat-exchangepipe according to claim 1, wherein in a transverse cross section acrossan axis of the metal pipe, a difference between an average area ratio ofthe metal fibers in a center circle part corresponding a half of an areaof the metal porous body and an average area ratio of the metal fibersin a whole of the transverse cross section is 5% or less.
 4. A producingmethod of a heat-exchange pipe, comprising a precursor formation step ofstacking a plurality of metal fibers to form a precursor, an in-pipecharging step of pushing the precursor from one end of a metal pipe tocharge into the metal pipe, and a sintering step of sintering the metalpipe in a state of charging the precursor, wherein the precursor beforethe in-pipe charging step is formed such that an outer diameter in astate where the metal fibers are stacked is larger than an innerdiameter of the metal pipe.
 5. The heat-exchange pipe according to claim2, wherein in a transverse cross section across an axis of the metalpipe, a difference between an average area ratio of the metal fibers ina center circle part corresponding a half of an area of the metal porousbody and an average area ratio of the metal fibers in a whole of thetransverse cross section is 5% or less.
 6. The heat-exchange pipeaccording to claim 1 wherein the metal porous body further includesmetal powder particles bonded to the metal fibers.
 7. A heat-exchangepipe comprising a metal pipe, and a porous body which is configured bysintering a plurality of metal base substances and bonded to aninner-wall surface of the metal pipe, wherein the metal base substancesincludes metal fibers, and the metal fibers bonded to the inner-wallsurface partially leave from the inner-wall surface.
 8. Theheat-exchange pipe according to claim 7 wherein the metal basesubstances further include metal powder particles.
 9. The heat-exchangepipe according to claim 8 wherein a ratio of the metal powder particlesin the metal base substances is 15% by mass or less.
 10. Theheat-exchange pipe according to claim 8 wherein a particle diameter ofthe metal powder particles is 5 μm or more and 500 μm or less.
 11. Theheat-exchange pipe according to claim 7 wherein the metal basesubstances are made of aluminum or aluminum alloy, and are joined by abase substance joint part contains a eutectic-element compound includingeutectic element that eutectic-reactions with Ti—Al type compounds andAl.
 12. The heat-exchange pipe according to claim 7, wherein a ratio L/Rbetween a length L and a fiber diameter R of the metal fibers I 10 ormore and 500 or less.